Why Tasers sometimes fail to stop suspects — and what weight has to do with it

Multiple Taser deployments failed to stop Pamela Cisneros, 49, during a roughly four-minute standoff in Times Square last Monday, after she allegedly stabbed two people. The attack left a 32-year-old woman dead and a 68-year-old man wounded.

"As multiple officers discharged Tasers, which proved to be ineffective, the subject continued to advance toward our officers with the knives," Jessica Tisch, New York City police commissioner, said in a news conference that evening. 

When the Tasers failed to subdue Cisneros — who stated, "I’m not dropping anything. I would rather kill both of you" — two officers opened fire, striking her. Cisneros was taken to Bellevue Hospital, where she was pronounced dead.

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The incident sparked broader questions about why Tasers sometimes fail and whether obesity or body composition can impede their effectiveness.

A standard Taser is designed to fire two small, barbed probes connected to the device by insulated, conductive wires, according to Axon, the manufacturer.

"Electrical pulses travel along those wires and into the body, triggering involuntary muscle contractions," Axon’s website states. "For NMI to occur, it is best that two probes make contact 12 inches (30 cm) or more apart."

Steve Keller, a retired police sergeant in Blue Ash, Ohio, said the most common causes of Taser failure include clothing, probe placement, substance abuse by the perpetrator and connectivity between probes.

However, obesity can affect the Taser, he said, as a large layer of body fat could interfere with the connectivity.

"The purpose of the Taser is neuromuscular in capacity," Keller told Fox News Digital.

"Your large muscle masses are your back and thighs. Officers are trained to aim for those areas," he said, just as they are also trained to adjust their aiming for clothing and the distance between them and the subject.

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If one of the probes hits the abdomen and the person is obese, it can affect the connectivity of the two probes, according to Keller.

"If one probe hits the person and the other probe misses, the Taser will not work," he said.

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For example, if one probe hits a subject in the thigh and the other probe hits a thick bubble jacket, there’s a good chance the officer won’t have good connectivity, Keller said.

"The same could be considered if there is a large layer of body fat — they could still feel it, but it might not be as effective."

Referring to Cisneros’ case, Keller emphasized that mental health may also play a significant role in how a person responds to a Taser.

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Tisch confirmed at the press conference that the suspect had a documented mental health history with the NYPD, with one incident in 2018 and another in 2019.

Dr. Marc Siegel, Fox News senior medical analyst, agreed that body composition can affect the Taser’s effectiveness.

"Tasers are much more effective for muscle than fat because muscle conducts electricity much better, and the Taser delivers a high voltage," he said. "In an obese person, it is more difficult to find an area that conducts electricity."

Fox News Digital reached out to Axon, the NYPD and obesity organizations requesting comment.